The invention relates to a power nut runner of the type comprising a rotation motor for driving an output shaft via a torque responsive release clutch including a driving clutch half, a driven clutch half, and a cam mechanism for transferring torque between the driving clutch half and the driven clutch half, wherein a first one of the driving and driven clutch halves is axially movable by the cam mechanism in a release direction from an engagement position to a release position, wherein a spring is arranged to bias and displace the first clutch half in an engagement direction, and wherein a clutch release detecting device is provided which is cooperative with the movable first clutch half.
In prior art nut runners of the above type, described for instance in U.S. Pat. Nos. 4,838,364 and 5,201,374, there are provided clutch release detecting devices including an activation rod extending axially through the rotor of the motor. Since the activation rod is not rotationally locked to the rotor, there will always be a difference in speed between the rod and the rotor which inevitably results in a frictional wear of the rod. Moreover, in most tools of this type there is employed a speed reduction gearing between the motor and the clutch, which means that there is also a difference in speed between the rotor and the activation rod support point on the clutch. This amplifies the problem of frictional wear of the rod, and despite an adequate surface hardening of the rod, there is still a problem with a limited service life of the device.
In U.S. Pat. No. 4,231,270, there is described a power screw driver in which a micro switch is actuated by one part of a torque limiting clutch provided between the ring gear of a planetary reduction gearing and the tool housing. This concept, however, is less advantageous in that the release detecting switch is activated by a clutch which is not an in-line clutch, i.e. the clutch does not transfer the driving torque. This results in a slower and less accurate release action and release detection.
In U.S. Pat. No. 3,608,686, there is described a torque responsive in-line clutch with an overload detecting micro-switch intended for preventing damage on machine tool parts by initiating disconnection of a drive motor. A disadvantage inherent in this device is that there is an indistinct action of the switch due to a rather short and slow axial release movement of the clutch part. This results in a less accurate release detecting signal. Another disadvantage of this known device is the continuous sliding action between the stationary micro-switch arm and the rotating clutch, which inevitably results in a frictional wear of these parts.
A disadvantage also relating to the clutch operated switch shown in U.S. Pat. No. 4,231,270 resides in the fact that the release movement of the clutch is rather short and that the switch has to be activated somewhere during that movement. Due to this short activation movement, the switch has to be very carefully adjusted to ensure a proper activation. This makes the release detecting and power shut-off mechanism rather sensitive and less reliable.
The primary object of the invention is to accomplish a power nut runner by which the above mentioned problems are avoided by providing a torque transferring clutch with a release detecting device which provides a distinct and prompt power shut-off initiating movement.
Further objects and advantages of the invention will appear from the following specification and claims.
A preferred embodiment of the invention is below described in detail with reference to the accompanying drawing figures.